This invention relates to the incorporation of various treatment agents into wood composite products such as oriented strand board, medium density fiberboard, fiberboard and particleboard. The invention also relates to the method of manufacturing wood based composite products whereby treatment compositions are added to the wood furnish prior to drying, forming and pressing into a finished board or panel product. (A “wood furnish” is defined as wood strands, chips, particles, flakes or fibers. “Wood particles” are defined broadly in this specification to include webs of splintered wood formed by twisting or crushing billets of wood, as well as other forms of wood particles. A wood treatment composition can be, for two examples, a fire retardant agent or a wood preservative, as well as other treatment agents.) The invention further relates to the products made by these processes.
The production of wood based composite panel products has increased dramatically in recent years. Oriented strand board (OSB) production exceeded that of plywood in 2000. In order to continue this new growth, additional uses for OSB need to be developed. Composite wood products find application in the construction of residential housing and commercial buildings. Common applications for these products include roof sheathing, wall sheathing, flooring, structural insulated panels and engineered wood components such as I-joists. With the ever-expanding production capacity of wood based composites there is a critical need to find additional uses. One such possibility is for structural and non-structural building components to be made resistant to fire. However, by virtue of their lignocellulosic composition, wood based composites are susceptible to combustion.
Chemical preservatives and fire retardant treatments are readily available for solid lumber and plywood. Such chemical treatments are applied to lumber and plywood using vacuum pressure processes to ensure uniform distribution of the active ingredients throughout the wood components thereby guaranteeing optimum performance.
Historically, attempts to incorporate chemical treatments into wood based composites using similar technology have failed for economic reasons or more commonly because of technical problems associated with irreversible and excessive swelling of the treated panels and severe loss of structural integrity.
The incorporation of a wood preservative in aqueous form directly into green wood particles, without first drying the wood particles, is disclosed in U.S. Ser. No. 09/550,027, filed Apr. 14, 2000. That disclosure also provides wood treatments that stabilize the dimensions of the wood composite when it is exposed to environmental moisture, preventing the wood composite products from swelling. Similar incorporation of a fire retardant treatment directly into green wood particles, without first drying the wood particles, is disclosed in U.S. Ser. No. 10/038,522, filed Oct. 23, 2001.
Additional discussion of treatment of wood products is found in U.S. Published Patent Application No. 20030026942, published Feb. 6, 2003, U.S. Ser. No. 60/322,644, U.S. Ser. No. 60/288,136, and U.S. Ser. No.: 10/251,615, filed Sep. 20, 2002, all the contents of which are incorporated by reference here.